Brush mounting for small commutator type motors



March 13, 1962 D; w. SIEVERT 3,025,421

BRUSH MOUNTING FOR SMALL COMMUTATOR TYPE MOTORS Filed June 27, 1958F/Gfl. 3/ INVENTOR.

7 g4 I I X 0AM PMS/[VHPT 4 L $4 E 'f 47 I 4a 7 5a ATTORNEYS trite Stats3,525,421 Patented Mar. 13, 1962 ice 3,025,421 BRUSH MOUNTING FDR SMALLCOMMUTATGR TYPE MOTORS Dale W. Sievert, Rockford, 111., assignor toBarber-Cob man Company, Rockford, 111., a corporation of Illinois FiledJune 27, 1958, Ser. No. 744,983 3 Claims. (Cl. 310-445) The presentinvention relates to the mounting of carbon brushes in a motor assemblyand more particularly to a mounting arrangement for a non-cumulative,constant tension spring which is especially suited to small motors ofcompact design. Where, in this specification and in the subjoinedclaims, reference is made to a non-cumulative, constant tension springthese terms are employed to designate a spring of the well known Negatortype, i.e. a spring every increment of which requires an equal force tostraighten it, such a spring being produced by drawing or passing astrip of metal between two forming elements to bend the strip partiallyso that every increment of the spring is bent on an equal radius.Inasmuch as every increment of the spring is equally stressed and bent,the force required to straighten any given portion of the spring isexactly the same as the force required to straighten any other portionof the spring. Therefore, in a spring of the Negator type, theresistance to straightening or drawing out of the spring isnon-cumulative.

In the past, attempts have been made to employ noncumulative, constanttension springs for applying constant take-up pressure to carbon brushesin commutator type motors. However, the special problems existing incompact miniature motors and the need for reliability have preventedsprings of this type from being fully utilized.

It is the primary object of the present invention to provide a brushmounting for small motors which is characterized by a high degree ofreliability and long life, a life safely exceeding that of the remainderof the motor. More specifically, it is an object of the presentinvention to provide a brush mounting arrangement for a non-cumulative,constant tension spring in which there is no danger of breakage of thespring due to concentrated forces being developed in the spring. It is arelated object to provide a brush mounting arrangement having anoncumulative, constant tension spring so arranged as to per mit longbrush travel, and therefore maximum take-up for brush wear, withoutsubjecting the spring to sharp bending or other concentrated stress,especially at the limits of travel.

It is another object to provide a non-cumulative, constant tensionspring brush mounting Which fully and efficiently utilizes the annularspace in the motor casing surrounding the commutator, space which islargely Wasted in conventional designs. Specifically, it is an object toprovide a symmetrical double non-cumulative, constant tension springarrangement in which the spring anchoring posts are on opposite sides ofand straddle the commutator recess.

It is a further object related to the foregoing to provide anon-cumulative, constant tension spring brush mounting which isespecially suited to motors in which the radial brush space is severelylimited.

In one of its aspects, it is an object of the present invention toprovide a novel commutator assembly which may be paired with a similarassembly to provide a brush supporting ring arrangement for nesting inthe motor housing in the annular space surrounding the commutator andforming a rigid structural part of the motor frame. It is a relatedobject to provide a structure of the above type which requires a minimumof structural hardware for securing the component pieces together.

It is another object to provide a commutator brush assembly which may bereadily removed for service or replacement and which enables productionof a small motor at minimum cost.

Other objects and advantages will become apparent upon reference to theattached detailed description and upon a review of the drawing in which:

FIGURE 1 is a side view of a motor employing the present invention withthe end portion in vertical section.

FIG. 2 is a transverse section of the motor of FIG. 1 taken along theline 22 therein.

FIG. 3 is an enlarged fragmentary view similar to FIG. 2 to bring outsome of the details of the brush rigging.

FIG. 3a shows the non-cumulative, constant tension spring in extendedand relaxed positions respectively.

FIG. 4 is a top view in partial section looking along the line 4-4 inFIG. 3.

FIG. 5 is an enlarged perspective of the brush guide shown in thepreceding figures.

While the illustrative form of the present invention has been shown inthe drawing and described herein in detail, it will be understood that Ido not intend to limit myself to this embodiment but intend to cover allmodifications and equivalent constructions falling within the spirit andscope of the appended claims.

Turning now to FIG. 1 there is shown a motor 10 having a housing 11including an end cap 12. Telescoping within the housing 11 is an annularfield structure 13, the parts being secured together by longitudinalscrews 14, 15 to form a stator assembly.

Centered within the field structure 13 is an armature 20 having a shaft21 and a commutator 22, with the shaft journaled in bearings 23. Thecommutator and housing define an annular space 25 of small cross sectionhereinafter referred to as the commutator recess.

Arranged within the annular space 25 is a brush assembly generallyindicated at 30 having a mounting plate of annular shape comprised oftwo semi-annular portions 31, 31a. Taking the mounting plate 31 and itsassociated brush assembly by way of example (FIG. 3), it will be seenthat the mounting plate carries a hollow brush guide 32 enclosing abrush 33 which is movable radially therein. The brush guide 32preferably has a dovetailed mounting portion 34 which is integrallymolded in the mounting plate 31, which latter may be made ofthermosetting plastic material. To provide convenient electricalconnection, a terminal plate 35 is secured to the front surface of thebrush guide and connected to the brush by a pigtail 36.

In accordance with the present invention, an inverted V-shapednon-cumulative, constant tension spring is provided which is looped overthe brush 33 at its central portion and anchored in supporting postswhich lie on opposite sides of the commutator. More specifically, Iprovide a V-shaped non-cumulative, constant tension spring 40 which, asshown in FIG. 3, has a rounded crotch portion 41 and side portions 42,43 terminating in end curls 45, 46 respectively. The latter are woundabout posts 47, 43. These posts are preferably in the form of headedscrews threaded into bushings 51, 52 which are molded integrally in themounting. plate, each screw being surrounded by a sleeve or spacer 53 toprovide clearance for the curled ends of the spring as well as toprovide an antifriction surface about which the spring may rotate as itcurls or uncurls.

For the purpose of providing exit clearance for the side portions 42, 43of the spring, the brush guide is slotted as indicated at 55, 56, withthe slots extending almost to the lower end of the guide.

It is one of the features of the present invention that the posts 47, 48which mount the curled ends of the noncumulative, constant tensionspring are spaced wide apart within the motor housing at points lying onopposite sides of the commutator or commutator recess. Preferably, theposts are positioned in the end portions of the respective semi-annularmounting plates. As brought out in FIG. 3, the location of the posts inthe present instance is such that a line 6%) which interconnects themintersects the commutator.

Viewed in a slightly different light, the post spacing is sufficientlywide so that the two side portions 4-2, 43 of the spring are atapproximate right angles with respect to one another. In the presentembodiment this angle varies from a minimum of approximately 70 when thespring is fully extended, as with a new brush, to approximately 120 whenthe spring is in its lowered position and with the brush near the end ofits useful life.

It is found that this arrangement, in practice, is accompanied by anumber of important advantages. In the first place, my observations showtha reliability is greatly improved and that spring breakage issubstantially eliminated. Thus the spring is required to undergo only alimited bending or fiexure in covering the entire range of movement, achange of only approximately 50 in included angle. Materialsconventionally employed in the making of small non-cumulative, constanttension springs can accommodate such change in angle without subjectingthe material to any undue stress, i.e., stress which is localized andwhich runs the risk of breakage. Moreover, it is found that thearrangement is such as to give a long stroke of brush take-up movement,with the force being at all times radially centered on the brush and ofsubstantially non-cumulative, constant tension over the range ofmovement. This permits longer brushes to be used than would otherwise bepossible thereby enabling a longer period of use before replacement.Since balanced forces are maintained over the entire stroke of thebrush, there is no risk that the brush will become skewed or hung upwithin the brush guide.

It will be understood by one skilled in this art that the arrangementdescribed enables maximum and most eflicient utilization of thecommutator recess, i.e. the annular space available between thecommutator and the housing. Thus it will be noted in FIG. 2 that thesides of the springs form chords of maximum length. It can be shown thatthis arrangement not only permits longer springs to be employed but moreeffective utilization of the non-cumulative, constant tension action orphenomenon.

With regard to the non-cumulative, constant tension spring itself, themaking of springs of this type is within the skill of the art (see forexample, such patents as Lermont Pat. No. 2,609,192 of September 2,1952, Lermont Pat. No. 2,301,669 of August 6, 1957, and Cook Pat. No.2,647,743 of August 4, 1953), the spring in the relaxed state occupyingthe position shown in full lines in FIG. 3a.

if desired, the crotch portion 411 of the spring may be curved as shownat 41 in FIG. 3, with a sharper bend I on each side of the curve forengaging the shoulders of the upper end of the brush and to insure thatthe spring remains centered on the brush. Over the useful range orstroke, the change in the included angle tends to be accommodated by achange in the curvature of the curved portion 41 rather than by bendingat the shoulder-accommodating portions of the spring. The setting up oflocalized stress at the corners is avoided.

While the invention has been described thus far in connection with onlyone of the brush assemblies, it is one of the features of the presentinvention that the companion assembly, mounted on plate 314:, isidentical in every way, with corresponding parts having correspondingreference numerals with subscript a. In accordance with one of thedetailed features of my device, the

mounting plates 31, 31a, although identical, have ends which areinterfitting or interlocked. The latter is brought about by making theends of each of the mounting plates respectively non-symmetrical, themounting plate 31 having an inwardly offset tongue at one end and anoutwardly offset tongue 66 at the other. These mate respectively withcorresponding tongues 66a, 65a on the other piece as shown. The resultis to produce a continuous annular plate, which is substantiallyselfsupporting and which forms an integral part of the motor structure.Because of the interfitting, it is possible to secure both brushassemblies in place within the housing with only two screws 71, 71a(FIG. 2).

Experience through the years with miniature commutator-type motors hasindicated that the brushes and brush rigging constitute the weakest linkin the conventional design, the portion of the motor which is mostlikely to fail and which requires most frequent maintenance. Bycontrast, the present arrangement requires substantially no maintenance,giving long brush life and reliable operation over long periods of timeand enabling motors of the present design to be employed in the mostexacting commercial and military applications.

I claim as my invention:

1. In a motor, the combination comprising a rotor having a commutator, astator surrounding said commutator and spaced therefrom to provide acommutator recess between said commutator and stator; a brush withinsaid recess and having its inner end engaging said commutator; a brushguide mounted within said recess for guiding said brush for radial takeup with respect to said commutator; a non-cumulative, constant tensionspring of the inverted V shape type within said recess and having acrotch portion looped over the outer end of said brush and havingsubstantially straight side portions disposed on opposite sides of saidbrush guide, said side portions terminating in curled end portions; anda pair of supporting posts within said recess each surrounded by acurled end portion of said spring with said curled ,end portions free tocurl and uncurl about said supporting posts, said posts being spacedsubstantially away from said brush guide at opposite sides thereof sothat the substantially straight side portions of said spring extendgenerally chordwise within said recess, and said posts beingsymmetrically spaced within said recess so that a line joining thesubstantially center portions of said supporting posts passes throughsaid commutator.

2. In a motor, the combination set forth in claim 1, wherein the sideportions of said spring extend at approximate right angles to oneanother.

3. In a motor, the combination set forth in claim 1, and including asemi-annular mounting plate within said recess, with said brush guidemounted on said plate near the center thereof, and with the saidsupporting posts mounted on said plate near the opposite ends thereof.

References Cited in the file of this patent UNITED STATES PATENTS2,324,299 Haifley July 13, 1943 2,632,860 Agron Mar. 24, 1953 2,848,633Atamian Aug. 19, 1958 2,881,3 9 Fisher Apr. 7, 1959 FOREIGN PATENTS658,776 Germany Apr. 11, 1938 OTHER REFERENCES Electrical Manufacturing,February 1956, pages 95, 96, 97, published by NcGraw-Hill, New York,N.Y.

Product Engineering, July 1, 1949, pages 136 to 139.

